1. Field of Invention
The present invention relates to a transflective pixel structure. More particularly, the present invention relates to a transflective pixel structure capable of improving image quality.
2. Description of Related Art
The rapid advancement of the multimedia society mostly benefits from the rapid progress of semiconductors and display apparatuses. As to the displays, cathode ray tube (CRT) has been leading the display market because of its outstanding performance and cost-saving characteristic. However, in the environment wherein individuals operate most terminals/display apparatuses at their desks, or from the point of view of environmentalism, if estimated with the energy-saving trend, the cathode ray tubes still have many problems in space-using and energy consumption, and cannot provide solutions for the requirements of lighter, slimmer, smaller, and energy-saving devices. Thus, thin-film transistor liquid crystal displays (TFT-LCD) having characteristics of high resolution, space-saving, low power consumption, low radiation etc have become the mainstream of display market gradually.
Generally, liquid crystal displays may be classfied into transmissive LCDs, reflective LCDs, and transflective LCDs according to their differences in light sources usage and array substrate. The transmissive LCDs use mainly back light as light sources, and the pixel electrodes on the array substrates of the transmissive LCDs are transparent which allows the back light to penetrate; the reflective LCDs use mainly front light or external light as light sources, and the pixel electrodes on the array substrates of the reflective LCDs are electrodes made from metal or other materials with excellent reflective characteristic which may reflect front light or external light efficiently; and the transflective LCDs may use both back light and external light as light sources, the pixels thereon can be divided into transmissive area and reflective area, the transmissive area has transparent electrodes which allows the back light to penetrate, and the reflective area has reflective electrodes which can reflect external light.
FIG. 1 is a structural diagram of a conventional liquid crystal display unit with dual cell gap. Referring to FIG. 1, the liquid crystal display unit 100 is divided into two areas, a transmissive area T and a reflective area R. In another aspect, the liquid crystal display unit 100 comprises a first substrate 110, a thin-film transistor 120, a dielectric layer 130, a transparent electrode 140, a reflective electrode 150, a liquid crystal layer 160, a spacer 170, a color filter film 180, and a second substrate 190.
As shown in FIG. 1, the thin-film transistor 120 is disposed on the first substrate 110; the dielectric layer 130 is disposed on the thin-film transistor 120 and the first substrate 110; the transparent electrode 140 and the reflective electrode 150 are both disposed on the dielectric layer 130 and are respectively located in transmissive area T and reflective area R; the color filter film 180 is disposed on a bottom surface of the second substrate 190; the liquid crystal layer 160 is disposed between the transparent electrode 140 and the reflective electrode 150 over the first substrate 110 and the color filter film 180; the spacer 170 is disposed on the transparent electrode 140 or the reflective electrode 150 to keep the cell gap of the liquid crystal display unit 100.
It's noted that the cell gap of transmissive area T is twice as the cell gap of reflective area R. In the reflective area R, the light enters the liquid crystal display is reflected out of the liquid crystal display unit 100 by the reflective electrode 150. In the transmissive area T, the light enters the liquid crystal display passes through the liquid crystal display unit 100 directly. The propagating distance of the light in the reflective area R and in the transmissive area T is substantially identical. Thus, the transmittance of the reflective area R is substantially identical to the transmittance of the transmissive area T.
FIG. 2 is a simulative diagram illustrating the transmittance of the liquid crystal display unit with dual cell gap. Referring to FIG. 2, the transmittance of the reflective area R and the transmittance of the transmissive area T are substantially the same under different bias voltages. In other words, the transflective LCDs with dual cell gap have better display quality. However, since the cell gap of the transmissive area T and the cell gap of the reflective area R are different, a taper formed at the join of the transparent electrode 140 and the reflective electrode 150 will cause inconsistent liquid crystal rubbing in certain area or uneven electric field, and which may further cause light leakage in transflective LCDs with dual cell gap. Moreover, the taper formed at the join of the transparent electrode 140 and the reflective electrode 150 will decrease the aperture ratio of transflective LCDs with dual cell gap.
FIG. 3 is a structural diagram of a conventional liquid crystal display unit with single cell gap. Referring to FIG. 3, the liquid crystal display unit 200 is similar to the liquid crystal display unit 100 shown in FIG. 2, the difference is that in the liquid crystal display unit 200, the cell gap of the transmissive area T is substantially identical to the cell gap of the reflective area R. Even though there is no light leakage or aperture ratio decrease problem in transflective LCDs with single cell gap since there is no taper formed between the transparent electrode 240 and the reflective electrode 250, but under the same driving voltage, the display quality of the transflective LCDs with single cell gap is not ideal due to the difference between the transmittance of the reflective area R and the transmittance of the transmissive area T.
FIG. 4 is a simulative diagram illustrating the transmittance of the liquid crystal display unit with single cell gap. Referring to FIG. 4, the transmittance of the reflective area R and the transmittance of the transmissive area T are quite different under the same bias voltage. As described in FIGS. 3 and 4, such liquid crystal display unit 200 with single cell gap cannot manage both the transmittance of the reflective area R and the transmittance of the transmissive area T efficiently.